5. The composition of claim 4 wherein the vegetable derived wax is derived
from soybean.

6. The adhesive of claim 2 where the ethylene vinyl acetate copolymer has
a vinyl acetate content of from about 4 to about 33 wt % and a melt index
of from about 400 to about 2500 g/10 min and the ethylene n-butyl
acrylate copolymer has a butyl acrylate content of about 28 to about 33%
and has a melt index of about 40 to about 900 g/10 min.

7. The adhesive of claim 1 wherein the tackifier is selected from the
group consisting of styrenated terpenes, terpene phenolics, aromatic
hydrocarbons, aromatic/aliphatic hydrocarbons, hydrogenated tackifiers,
and alphamethylstyrene

8. The adhesive of claim 1 comprising5 to 35 wt % of an ethylene vinyl
acetate copolymer has a vinyl acetate content of from about 4 to about 33
wt % and a melt index of from about 400 to about 2500 g/10 min,5 to 30 wt
% of an ethylene n-butyl acrylate has a butyl acrylate content of about
28 to about 33% and has a melt index of about 40 to about 900 g/10 min,5
to 40 wt % of a soy wax,0 to 20 wt % of a paraffin wax, and10 to 45 wt %
of a styrene terpene tackifier and/or a terpene phenolic tackifier.

9. An article of manufacture comprising the adhesive of any of claims 1, 3
or 8.

10. The article of claim 9 which is a packaging article.

Description:

[0002]Hot melt adhesives are applied to a substrate when molten, and then
placed in contact with a second substrate. The adhesive cools and hardens
to form a bond between the substrates. Hot melts are widely used for
industrial adhesive applications such as product assembly and packaging.
The latter include case and carton sealing.

[0003]Hot melts for packaging applications such as case and carton sealing
are typically composed of a polymer, a diluent or tackifier, and a wax.
One function of the wax component, due to its low molecular weight, is to
lower viscosity. Currently used packaging adhesives comprise
petroleum-derived waxes such as paraffin and microcrystalline wax. The
lower molecular weight of paraffin wax makes it a primary choice when
formulating low application temperature adhesives.

[0004]Recently, however, due to the limited supply of paraffin wax,
attention has turned to the use of natural waxes. Of the natural waxes,
the lowest cost materials are based on highly hydrogenated triglycerides
Borsinger et al., U.S. Pat. No. 6,890,982 B2, discloses hot melt
adhesives containing a vegetable derived wax. The adhesive compositions
of Borsinger et al. have a melt viscosity of from about 1000 to bout 5000
cps at 350° F. The high levels of hydrogenation (low iodine
values) are necessary to elevate the melting point closer to paraffin.
Unfortunately, since triglycerides are of much higher molecular weight
than paraffin--about 890 Da for the pure tristearate of glycerin, versus
430 Da for a typical paraffin wax, adhesives using highly hydrogenated
triglycerides have higher viscosity making them unsuitable for
application at low temperatures.

[0005]A need exist for hot melt adhesives that can be applied at low
temperatures, i.e., that have an application viscosity that allows for
application at low temperatures (at temperatures less than 300°
F.), and that can be formulated with reduced dependency on the use of
paraffin wax. The invention fulfills this need.

SUMMARY OF THE INVENTION

[0006]It is an object of the present invention to provide a low
application temperature hot melt adhesive containing a vegetable derived
wax. The adhesives of the invention may be used to bond one substrate to
a second substrate after the adhesive has been applied to the substrate
surface at a temperature of below 300° F. down to 200° F.
or below. In one embodiment, the adhesive is formulated for application
at a temperature of below about 280° F. In another embodiment, the
adhesive is formulated for application at a temperature of below about
250° F. The adhesive compositions of the invention comprise a
vegetable derived wax. In one embodiment, the adhesive compositions of
the invention comprise a vegetable derived wax and a paraffin wax. In one
preferred embodiment, a mixture of a soy wax and a paraffin wax is used.

[0007]The adhesive composition can be applied to articles such as paper,
paperboard and the like to bond them together for use in consumer and
other packaged goods applications.

[0008]Yet another embodiment of the invention provides articles
manufactured using the hot melt adhesive of the invention. In a preferred
embodiment the article is a packaging article.

[0009]Another aspect of the invention is directed to a method of sealing
and/or making or forming a case, a carton, a tray, a box or a bag or
other packaging article. These methods comprise using a low application
temperature hot melt adhesive that comprises a soy wax. Also provided are
articles manufactured using such a soy wax-containing adhesives.
Encompassed are cartons, cases, trays, bags and the like that can be used
for packaging products. Such articles typically comprise cardboard or
paperboard which has been adhered by such hot melt adhesives. The
invention also provides packaged articles contained within a carton,
case, tray or bag, in particular packaged food, wherein the carton, case,
tray or bag comprises a soy wax-containing adhesive.

[0010]Yet another aspect of the invention is directed to a process for
bonding a substrate to a similar or dissimilar substrate comprising
applying to at least one substrate a molten low application temperature
hot melt composition which comprises a soy wax and bonding said
substrates together.

DETAILED DESCRIPTION OF THE INVENTION

[0011]All references cited herein are incorporated in their entireties by
reference.

[0012]Hot melt adhesives are widely used in packaging industry to seal
cardboard cases, trays, and cartons. Some of these operations require hot
melt adhesive with exceptional high heat resistance (ability to maintain
fiber tear at high temperature) without compromising good cold
temperature performance. One example is to package freshly based goods at
temperature greater than 140° F. and its subsequent storage at
freezer temperatures of -20° F. Another example that requires hot
melt adhesives with good heat and cold resistance is in the process of
shipping sealed cases, cartons or trays by trucks or railway. The
temperature in a truck could be very high (up to 145° F.) in the
summer or very low in the winter (-20° F.). The hot melt adhesives
used should be strong enough such that the sealed containers will not pop
open during the transportation process.

[0014]A low application temperature hot melt adhesive is an adhesive that
can be applied to a substrate surface at a temperature of less that
300° F. and then used to bond the substrate to a second substrate
surface. Such adhesive do not require heating to temperatures greater
than 300° F. in order to reduce viscosity prior to application.

[0015]It has now been discovered that highly hydrogenated oils such as
palm and soybean can be converted into a wax (a vegetable derived wax)
that can be used effectively as substitutes for conventional waxes in the
formulation of low application temperature hot melt adhesive compounds.

[0016]A vegetable derived wax is defined herein as a wax derived from
renewable natural resource, such as from a plant source such as soybean,
cottonseed, corn, sunflower, canola and palm. More particularly a
hydrogenated oil comprising a triglyceride whose fatty acid components
have a range of carbon numbers, with stearic acid (C18) being the
most predominate. The term "soy wax" is used herein to refer to a wax
derived from soybeans.

[0017]The low application temperature adhesives of the invention comprise
an adhesive base polymer component, a tackifier component and a wax
component. In contrast to petroleum or synthetically derived waxes
currently used to formulate hot melt adhesives, the adhesives of the
invention are formulated using a vegetable derived wax. Examples of
vegetable derived waxes include waxes derived from soybean, corn,
cottonseed, rape, canola, sunflower, palm, coconut, crambe, linseed and
peanut wax. One embodiment uses a soybean derived wax. Soy waxes are
derived from fully hydrogenated soy oil and are essentially
triglycerides, which may be illustrated as:

[0018]It has now been discovered that low temperature applied hot melt
adhesives (applied at temperature below 300° F.) suitable for use
as a hot melt packaging adhesive can be formulated using soy waxes.
Advantages of using a low application temperature hot melt adhesive
includes reduced number and/or capacity of heating elements required in
the hot melt adhesive tanks, reduced volatile emissions, reduced risk of
burn injury, and reduced wear and tear on the application equipment.
While there are currently several low application temperature hot melt
adhesives available commercially, such as for example NSC 34-2125
(National Starch and Chemical Company), NSC 34-250A (National Starch and
Chemical Company), NSC 34-650A (National Starch and Chemical Company), HL
7000 (H. B. Fuller), and HL 7002 (H. B. Fuller), none of these low
application temperature hot melt adhesives contain a wax component that
comprises a vegetable derived wax such as soy wax.

[0019]The invention provides low application temperature hot melt adhesive
compositions wherein at least a portion of the wax component is a
vegetable derived wax. In one embodiment at least a portion of the wax
component is a hydrogenated soy wax. In another embodiment the entire wax
component is a vegetable derived wax. The adhesives of the invention are
particularly advantageous when used as packaging adhesives. The
formulated adhesive will typically have a viscosity of from about 1000 to
about 2500 cps at 250° F.

[0020]One embodiment of the invention is directed to a hot melt adhesive
that may be applied to a substrate in the molten state at a temperature
of less than 300° F., another substrate is brought in contact with
the molten adhesive, and upon cooling the substrates are bonded together.
In one embodiment the adhesive is applied at 280° F. or less. In
another embodiment the adhesive is applied at 275° F. or less. In
still another embodiment the adhesive is applied at 250° F. or
less. In yet another embodiment the adhesive is applied at 200° F.
or less.

[0021]As is demonstrated herein, hot melt adhesives based on hydrogenated
soy wax, in full or partial substitution of petroleum or synthetically
derived waxes currently widely used in the formulation of hot melt
adhesives based on ethylene vinyl acetate (EVA), ethylene n-butyl
acrylate (EnBA) and EVA/EnBA blends, show an excellent balance of high
and low temperature performance in packaging case and carton adhesives
and comparable to petroleum based paraffin wax, use of soy wax provides
excellent compatibility with various resins and ethylene copolymers that
exhibit longer open times coupled with good heat resistance.

[0022]Polymer selection is critical in determining the performance of the
formulated hot melt adhesives. A polymer with low glass transition
temperature usually shows good cold resistance, while a polymer with high
melt temperature is normally easier to formulate adhesives with good heat
resistance. The adhesives of the invention will preferably comprise at
least one ethylene polymer, and may comprise a blend of two or more
polymers. Preferred embodiments will comprise EVA, EnBA or blends there
of. Adhesives comprising about 5 wt % to about 30 wt % of an ethylene
n-butyl acrylate copolymer containing 28 to 33% butyl acrylate and having
a melt index 40 to 900 and about 5 to about 35 wt % of an ethylene vinyl
acetate copolymer containing 4 to 33% vinyl acetate and having a melt
index of 400 to 2500 comprise one preferred embodiment.

[0023]The adhesive compositions of this invention are tackified. The
tackifier component will usually be present in an amount of from about 10
wt % to about 45 wt %, more preferably from about 20 wt % to about 50 wt
%, even more preferably from about 20 wt % to about 40 wt %. These
include natural and synthetic resins. Natural resins include rosin, rosin
esters, and polyterpenes. Synthetic resins include C5 cyclic and acyclic
resins, aromatic resins, C9 resins, pure monomer resins such as those
based on alpha-methyl styrene, and copolymer resins of the above monomers
with each other and/or phenol. Preferred embodiments will comprise a
tackifier selected from styrenated terpenes, terpene phenolics, aromatic
hydrocarbons, aromatic/aliphatic hydrocarbons, hydrogenated tackifiers,
or alphamethylstyrene. Adhesives of the invention will typically comprise
from about 10 to 45 wt % of a tackifier. Styrenated terpene and terpene
phenolic tackifiers are particularly preferred.

[0024]The adhesives of the invention are formulated using a vegetable
derived wax. Examples of vegetable derived waxes include waxes derived
from soybean, corn, cottonseed, rape, canola, sunflower, palm, coconut,
crambe, linseed and peanut wax. One embodiment uses a soybean derived
wax. Soy waxes a commercially available form Cargill, ADM and Bunge Oils.
The soy wax component wi typically be used in amounts of from about 5 wt
% to about 40 wt %.

[0025]In addition to a vegetable derived wax, the formulations of the
invention may also comprise a petroleum based or synthetic wax. Waxes
suitable for use in the present invention include paraffin waxes,
microcrystalline waxes, polyethylene waxes, polypropylene waxes,
by-product polyethylene waxes, Fischer-Tropsch waxes, oxidized
Fischer-Tropsch waxes and functionalized waxes such as hydroxy stearamide
waxes and fatty amide waxes. Paraffin waxes that can be used in the
practice of the invention include Okerin® 236 TP available from Astor
Wax Corporation, Doraville, Ga.; Penreco® 4913 available from
Pennzoil Products Co., Houston, Tex.; R-7152 Paraffin Wax available from
Moore & Munger, Shelton, Conn.; and Paraffin Wax 1297 available from
International Waxes, Ltd. in Ontario, Canada, Pacemaker available from
Citgo, and R-2540 available from Moore and Munger; and other paraffinic
waxes such as those available from CP Hall under the product designations
1230, 1236, 1240, 1245, 1246, 1255, 1260, & 1262. CP Hall 1246 paraffinic
wax is available from CP Hall (Stow, Ohio). Up to about 20 wt % of
paraffin wax may, if desired, by used.

[0026]Other compounds could be added that also do not affect physical
properties are pigments which add color, or fluorescing agents, to
mention only a couple. Additives like these are known to those skilled in
the art. Depending on the contemplated end uses of the adhesives, other
additives such as plasticizers, pigments and dyestuffs conventionally
added to hot melt adhesives might be included. In addition, small amounts
of additional tackifiers and/or waxes such as microcrystalline waxes,
hydrogenated castor oil and vinyl acetate modified synthetic waxes may
also be incorporated in minor amounts, i.e., up to about 10 percent by
weight, into the formulations of the present invention.

[0027]The adhesives of the present invention will preferably contain a
stabilizer or antioxidant. These compounds are added to protect the
adhesive from degradation caused by reaction with oxygen induced by such
things as heat, light, or residual catalyst from the raw materials such
as the tackifying resin. Among the applicable stabilizers or antioxidants
included herein are high molecular weight hindered phenols and
multifunctional phenols such as sulfur and phosphorous-containing phenol.
Antioxidants are typically used in amounts of up to about 1 wt %.

EXAMPLES

[0028]All adhesive formulations were prepared in single blade mixer heated
to 250° F. by mixing the components until homogeneous. The
adhesives were then subjected to various tests simulating successful
commercial applications.

[0029]Melt viscosities of hot melt adhesives were determined on a
Brookfield Thermosel viscometer using a No. 27 spindle.

[0030]Adhesion at 120° F., room temperature, 40° F.,
20° F., and 0° F. was determined by applying a half inch
wide bead of adhesive at 250° F. (or at 350° F. for NSC
34-2100) to a 2''×3'' piece of double fluted corrugated board, and
immediately bringing a second piece of corrugated board into contact to
form a bond. A 200 g weight was immediately placed on the top of the bond
for 2 seconds to provide compression. The specimens prepared were
conditioned at room temperature for overnight and then placed in oven or
refrigerators at different temperatures for 8 hr. The bonds were
separated by hand and the resulting fiber tear was recorded.

[0031]The heat stress test (HS) was following the loPP procedure. Two
bonds with glue line dimension of 2''×0.5'' was subjected to a 200
g or 300 g force, and placed in an oven starting at 125° F. to
140° F. for 8 hr and 24 hr respectively. The test results were
recorded as pass (two bonds past), fail (both bonds failed), or split
(one bond past and the other one failed) respectively.

[0032]The cloud point temperature is the temperature at which a component
begins to solidify or "cloud up" as it cools from a clear homogeneous
liquid phase to the semisolid phase. For example, for waxes, the cloud
point is usually close to the wax's melting point. Compatibility is
related to an adhesive's cloud point, where generally speaking, the lower
the cloud point the greater the compatibility.

Example 1

[0033]Compatibility of soy wax with adhesive formulations based on
ethylene vinyl-acetate copolymers having the formulation shown in Table 1
(Samples 1-5) was tested.